Elimination of pulsations in gas lines



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' INVFJVTOR.

June 28, 1949. F. M. STEPHENS 2,474,553

ELIMINATION OF PULSATIQNS IN GAS LINES Filed March 19, l946 Patented .1... 2a, 1949 ELIMINATION OF PULSATION S IN GAS LINES Foster M. Stephens, Los Angele's, Calif., assignor to The Fluor Corporation, Ltd., Los Angeles, Calii., a corporation of California Application March 19, 1946, Serial No. 655,409

5 Claims. (Cl. 230236) This invention has reference to the dampening or elimination ofpulsations in gas streams, particularly for the correction of pulsating flow created in gas lines by'a compressor or the like. Typically, the invention is applicable to the elimination of pulsations created by piston-type compressors in natural gas lines.

- My general object is to provide a simple arrangement of equipment constituting a resonant type acoustical system having predetermined resonating characteristics rendering it responsive to the pulsating gas flow in a manner resulting in virtually complete elimination of the pulsations. Briefly, the purposes of the invention are served by the simple requirement of a single closed chamber having restricted communication with the gas line from which pulsations are to be eliminated, the sizes of the chamber and restricted communication being predeterminedin the manner hereinafter explained. v

Generally speaking, the invention contemther variational form.

plates as the components 'of the resonator system, v

' a closed chamber of predetermined volume, but

otherwise shaped or proportioned as may be desired, and a restricted communication between the chamber and fiow line. which may be one of difierent types. As a first example, the restriction may take essentially the form of an orifice of predetermined size, contained in a connection whose length is sufliciently short as to create no effect interfering with the acoustical functions of the orifice itself. The orifice may be of fixed sizeand capable of replacement by different sized orifices in accordance with changing operating condition s. or the orifice may be contained in a valvetype fitting and thereby rendered adjustable, i. e. variable in size.

Instead of using an orifice type restriction in the communication between the chamber and gas line, I may employ an extended restricted passage in the nature of an acoustical inductance, formed for example by an elongated pipe having a diameter substantially smaller than the gas line. As a further alternate form of the restricted communication, I may use a fixed size or adjustable orifice together with an extended inductance passage.

As indicated, in whatever form used, the restricted connection together with the communicating closed chamber, presents an acoustical resonating system tuned to the frequency of the pressure pulsations and responsive in such phase relationship therewith as to convert the gas stream from pulsating to steady flow.

Embodiments of the invention and methods for Referring first to Fig. 1, the gas line l0 may connect with either the intake or discharge side of the compressor I I, since in either instance the compressor operation may, and is assumed to create by virtue of its piston-displacement, pres sure pulsations in the gas stream. When leading from the discharge side of the compressor, line I!) usually will contain a shut-off valve l2. It will be appreciated that when serving as the gas line leading to or from the usual natural gas compressor (single -acting or double-acting), pipe l0 may be of relatlvely'large size, e. g.8 inch diameter or larger.

The resonator system, generally indicated at I3, consists of the simple combination of a closed chamber or shell l4, and a restricted connection l5 between the chamber and line [0, desirably in such relation thereto that the path of communication through l5 is'i n the direction of the gas flow. Thus in Fig. 1, the gas is assumed to be discharged from the compressor into the T-fitting I 6 from which passage I5 is formed by a short a connection with the chamber. The connection contains a fitting II which, as previously indicated, may present a fixed size orifice, as for example in the conventional orifice plate, or a variable size orifice as provided by an adjustable or valve type fitting. For best results, it is preferred that the length of the connection between chamber l4 and the gas line I 0 shall be sufiiciently short that the rest'fictive eifect in the connection l5 shall be substantially entirely the restriction presented by the orifice, although it is to be understood that the connecting passage otherwise may be considerably smaller than the cross-sectional area of the gas line. Thus the orifice may be present in say 4 inch diameter connections at I8 and IS with the gas line and chamber.

The sizes of the chamber I4 and orifice at l5 may be predetermined to produce an acoustical system having proper resonant response to the pulsating fiow gas pulsation frequency, substantially in accordance with the following formula:

=Gas pulsation frequency per second. K =Velocity in centimeters per second of sound in the gas at its temperature and pressure. R=Radius of orifice in centimeters. v V=Volume of the chamber 14 in cubic centimeters.

This general equation holds true when the connection at II is sufficiently short as not to aflect the acoustical characteristics and functioning of the orifice as such.

In practical use of the formula, knowing the values for K (from tabulated data in the literature) and F from the cycle frequency of the compressor, an orifice of given size may be selected and the volume of the chamber calculated. Thus assuming air tube the gas (K value being 5475 cm. per second at C. and substantially atmospheric pressure) in which pulsations are created at a resonant frequency of 100 cycles per second, a circular orifice of 2 cm. diameter may arbitrarily be selected. Applying the formula and solving for V:

V=- substantially 6000 cu. cm. (5475 a The variational form of the invention shown in Fig. 3 is functionally similar to the described embodiment, but differs in its structural relation to the gas flow line. Here the latter, corresponding to line III in Fig. 1, is indicated at 23 to ex-' tend through the closed chamber 24 and to communicate therewith through an orifice within the chamber. The orifice may be formed at 25 either as an opening in the wall of the pipe, or as in the case illustrated, by providing a gap between spaced sections of the pipe.

In accordance with the variational form of the invention shown in Fig. 2, the resonant system 20 is formed by closed chamber 2| having an extended inductance-type connection 22 with the gas line It. Here the communication 22 may be in the form of an elongated pipe of substantially smaller diameter than the gas line ID, the latter typically having 8 inches or larger diameter and pipe 22 a diameter of 4 inches or smaller. Here the sizes of the chamber and length of pipe 22 (beyond a normally full open and non-restrictive valve 26 that may be placed adjacent the fitting l6a) are predeterminable by the following F=Gas pulsation frequency per second. K=Velocity in centimeters per second of sound in the gas at its temperature and pressure. R=Radius (inside) of pipe 22 in centimeters. L=Length of pipe 22 in centimeters. V=Volume of chamber 2| in cubic inches.

As a practical example of calculation, again assuming the gas to be air at 20 C. and substantially atmospheric pressure, pulsating at a frequency of 100 cycles per second, pipe 22 arbitrarily may be assigned a given length and diameter, for example a length of 100 cm. and inchamber 2 I:

the compressor and conducting the pulsating gas stream, and means comprising a closed chamber and a restricted orifice through which said cham-' ber is in communication with the pipe the sizes of said orifice and chamber being predetermined in substantial accordance with the formula:

wherein V=Volume of the chamber in cubic centimeters.

2. In combination with a gas compressor, apparatus for the removal of pulsations in a gas stream having pulsating flow created by the compressor.

' comprising a line pipe connected with the compressor and conducting the pulsating gas stream, and means comprising 'a closed chamber and an elongated smaller diameter pipe forming an acoustical inductance passage connecting' said line pipe with the chamber, the sizes of said smaller pipe and chamber being predetermined in substantial accordance with the formula:

wherein F Gas pulsation frequency per second;

=Ve1ocity in centimeters per second of sound in the gas stream atits temperature and pressure;

R=Radius of smaller pipe in centimeters;

L=Length of smaller pipe in centimeters;

V=Volume of the chamber in cubic centimeters.

3. In combination with a gas compressor, apparatus for the removalof pulsations in a gas stream having pulsating flow created by the compressor, comprising a line pipe connected with the compressor and conducting the pulsating gas stream, and a closed chamber having a restricted communication with said stream and forming with said communication an acoustical filter having a resonant frequency corresponding to the frequency of the dominating pulsations in said gas stream.

4. In combination with a gas compressor, apparatus for the removal of pulsations in a gas stream having pulsating flow created by the compressor, comprising a line pipe connected with the compressor and conducting the pulsating gas stream, a closed chamber, and means forming a restricted passage of smaller size than the pipe and chamber connecting said chamber with the pipe, said chamber and passage forming an acoustical filter having a resonant frequency corresponding to the frequency of the dominating pulsations in said gas stream.

5. In combination with a gas compressor, apparatus for the removal of pulsations in a gas stream side radius of 10 cm. Solving for the volume of having pulsating flow created by the compressor, REFERENCES CITED comprising a line pipe connected with the com- Wm H pressor and conducting the pulsating gas stream, ng fig z m are of record m the a closed chamber and an elongated smaller diameter pipe forming an acoustical inductance I UNITED STATES PATENTS passage connecting said line pipe with the cham- Datev her, said chamber and passage forming an acousggi a g Apr 7 1 tical filter having a resonantfrequency corre- 1 76710o Tannehflf "3 1 smndlng the frequency minating 1950'107 Quinn et 01:11:- Mar. 011934 sums in said stream 2,405,100 Stephens July 30, 1940 2,416,025 ,Shafl Feb. 18, 1947 FOSTER M. STEPHENS. 

